The present invention relates to an improved cross flow filtration apparatus of the type having an elongated filtration element housing and a cross flow filtration element disposed therein, and more particularly to an improved closure for such an apparatus. Generally, "cross flow" filtration technology, as opposed to "dead end" filtration technology, the feed water, in addition to having a portion pass through the filter medium, continually flows across the membrane or filter medium surface and exits through an outlet port at the opposite end of the apparatus. In contrast, with "dead end" filtration technology, there is no flow of feed suspension and/or solution relative to the filter media other than what passes through it.
Conventional cross flow filtration apparatus such as, but not limited to, reverse osmosis and ultrafiltration apparatus, includes a generally cylindrical housing, a cross flow filtration member disposed within such housing and means for closing off the ends of such housing. Various access openings are also provided so that feed solution can be supplied to the filtration element under pressure and concentrate and permeate can be withdrawn from the unit. Normally, the filtration element comprises a membrane member which is spirally wound around a central permeate tube.
In the prior art, the tendency in the art is to utilize fiberglass housings and to provide each end with a plug type fitting which is retained in sealing relationship relative to the housing by an 0-ring seal and a conventional retaining ring. Some of these retaining rings are conventional spiral or snap rings while others consist of segmented rings which are assembled in pieces and retained by screws or other threaded members. In apparatus having fiberglass housings, the various inlet and outlet ports are provided in the end plug itself. Additionally, some such apparatus includes a separate filter element support member positioned between a portion of the plug and the filtration element end to prevent the element from undesirable telescoping or axial movement.
Although many of the prior art cross flow filtration housings are constructed of fiberglass, some are constructed of stainless steel or other metal. While the filtration housings constructed of metal provide the capability of providing an inlet/outlet port positioned in a sidewall of the housing near one end, the filtration apparatus comprising metal housings continue to include end closures comprising a plug member retained in the end via a seal member and a conventional snap ring arrangement.
Current cross flow filtration apparatus and their closure mechanisms give rise to various problems and limitations. First, because of the relatively high pressures developed within the housing, the snap rings for retaining the end cap must be quite strong. To obtain the necessary strength, these are commonly constructed of a steel which tends to rust and oxidize. Although stainless steel rings are available, they generally have a much lower pressure rating. Secondly, each prior art closure mechanism consists of many parts, particularly if segmented retaining rings are utilized. Thus, because the closure apparatus must be removable to replace expended filter elements which have a much shorter useful life than the housing itself, the multiplicity of parts increases the replacement time. Thirdly, in filtration apparatus utilizing fiberglass housings, in which all of the inlet and outlet ports are provided within the end plug, it is necessary to remove or take off the high pressure pipe whenever the membrane elements are replaced. Fourthly, because it is sometimes difficult to determine whether the snap ring is properly seated, there is some danger that the closure could fail during operation of the apparatus. Accordingly, there is a need for a cross flow filtration apparatus with a closure assembly which solves these and other problems in the art.